Use of simple amino acids to form porous particles during spray drying

ABSTRACT

Particles having a tap density of less than 0.4 g/cm3 include a hydrophobic amino acid or salt thereof and a therapeutic, prophylactic or diagnostic agent or any combination thereof. Preferred particles include a phospholipid, have a median geometric diameter between about 5 and about 30 microns and an aerodynamic diameter between about 1 and about 5 microns. The particles can be formed by spray-drying and are useful for delivery to the pulmonary system.

BACKGROUND OF THE INVENTION

Aerosols for the delivery of therapeutic agents to the respiratory tracthave been described, for example, Adjei, A. and Garren, J. Pharm. Res.,7: 565-569 (1990); and Zanen, P. and Lamm, J.-W. J. Int. J. Pharm., 114:111-115 (1995). The respiratory tract encompasses the upper airways,including the oropharynx and larynx, followed by the lower airways,which include the trachea followed by bifurcations into the bronchi andbronchioli. The upper and lower airways are called the conductingairways. The terminal bronchioli then divide into respiratory bronchioliwhich then lead to the ultimate respiratory zone, the alveoli, or deeplung. Gonda, I. “Aerosols for delivery of therapeutic and diagnosticagents to the respiratory tract,” in Critical Reviews in TherapeuticDrug Carrier Systems, 6: 273-313 (1990). The deep lung, or alveoli, arethe primary target of inhaled therapeutic aerosols for systemic drugdelivery.

Inhaled aerosols have been used for the treatment of local lungdisorders including asthma and cystic fibrosis (Anderson, Am. Rev.Respir. Dis., 140: 1317-1324 (1989)) and have potential for the systemicdelivery of peptides and proteins as well (Patton and Platz, AdvancedDrug Delivery Reviews, 8: 179-196 (1992)). However, pulmonary drugdelivery strategies present many difficulties for the delivery ofmacromolecules; these include protein denaturation duringaerosolization, excessive loss of inhaled drug in the oropharyngealcavity (often exceeding 80%), poor control over the site of deposition,lack of reproducibility of therapeutic results owing to variations inbreathing patterns, the frequent too-rapid absorption of drugpotentially resulting in local toxic effects, and phagocytosis by lungmacrophages.

Considerable attention has been devoted to the design of therapeuticaerosol inhalers to improve the efficiency of inhalation therapies.Timsina et. al., Int. J Pharm., 101: 1-13 (1995); and Tansey, I. P.,Spray Technol. Market, 4: 26-29 (1994). Attention has also been given tothe design of dry powder aerosol surface texture, regarding particularlythe need to avoid particle aggregation, a phenomenon which considerablydiminishes the efficiency of inhalation therapies. French, D. L.,Edwards, D. A. and Niven, R. W., J. Aerosol Sci., 27: 769-783 (1996).Dry powder formulations (“DPFs”) with large particle size have improvedflowability characteristics, such as less aggregation (Visser, J.,Powder Technology 58: 1-10 (1989)), easier aerosolization, andpotentially less phagocytosis. Rudt, S. and R. H. Muller, J. ControlledRelease, 22: 263-272 (1992); Tabata, Y. and Y. Ikada, J. Biomed. Mater.Res., 22: 837-858 (1988). Dry powder aerosols for inhalation therapy aregenerally produced with mean geometric diameters primarily in the rangeof less than 5 μm. Ganderton, D., J Biopharmaceutical Sciences, 3:101-105 (1992); and Gonda, I. “Physico-Chemical Principles in AerosolDelivery,” in Topics in Pharmaceutical Sciences 1991, Crommelin, D. J.and K. K. Midha, Eds., Medpharm Scientific Publishers, Stuttgart, pp.95-115, 1992. Large “carrier” particles (containing no drug) have beenco-delivered with therapeutic aerosols to aid in achieving efficientaerosolization among other possible benefits. French, D. L., Edwards, D.A. and Niven, R. W., J. Aerosol Sci., 27: 769-783 (1996).

The human lungs can remove or rapidly degrade hydrolytically cleavabledeposited aerosols over periods ranging from minutes to hours. In theupper airways, ciliated epithelia contribute to the “mucociliaryescalator” by which particles are swept from the airways toward themouth. Pavia, D. “Lung Mucociliary Clearance,” in Aerosols and the Lung.Clinical and Experimental Aspects, Clarke, S. W. and Pavia, D., Eds.,Butterworths, London, 1984. Anderson, Am. Rev. Respir. Dis., 140:1317-1324 (1989). In the deep lungs, alveolar macrophages are capable ofphagocytosing particles soon after their deposition. Warheit, M. B. andHartsky, M. A., Microscopy Res. Tech., 26: 412-422 (1993); Brain, J. D.,“Physiology and Pathophysiology of Pulmonary Macrophages,” in TheReticuloendothelial System, S. M. Reichard and J. Filkins, Eds., Plenum,New York, pp. 315-327, 1985; Dorries, A. M. and Valberg, P. A., Am. Rev.Resp. Disease 146: 831-837 (1991); and Gehr, P., Microscopy Res. andTech., 26: 423-436 (1993). As the diameter of particles exceeds 3 μm,there is increasingly less phagocytosis by macrophages. Kawaguchi, H.,Biomaterials 7: 61-66 (1986); Krenis, L. J. and Strauss, B., Proc. Soc.Exp. Med., 107: 748-750 (1961); and Rudt, S. and Muller, R. H., J.Contr. Rel., 22: 263-272 (1992). However, increasing the particle sizealso has been found to minimize the probability of particles (possessingstandard mass density) entering the airways and acini due to excessivedeposition in the oropharyngeal or nasal regions. Heyder, J., J. AerosolSci., 17: 811-825 (1986).

Local and systemic inhalation therapies can often benefit from arelatively slow controlled release of the therapeutic agent. Gonda, I.,“Physico-chemical principles in aerosol delivery,” in: Topics inPharmaceutical Sciences 1991, D. J. A. Crommelin and K. K. Midha, Eds.,Stuttgart: Medpharm Scientific Publishers, pp. 95-117 (1992). Slowrelease from a therapeutic aerosol can prolong the residence of anadministered drug in the airways or acini, and diminish the rate of drugappearance in the bloodstream. Also, patient compliance is increased byreducing the frequency of dosing. Langer, R., Science, 249: 1527-1533(1990); and Gonda, I., “Aerosols for delivery of therapeutic anddiagnostic agents to the respiratory tract,” in Critical Reviews inTherapeutic Drug Carrier Systems 6: 273-313 (1990).

Controlled release drug delivery to the lung may simplify the way inwhich many drugs are taken. Gonda, I., Adv. Drug Del. Rev., 5: 1-9(1990); and Zeng, X., et al., Int. J. Pharm., 124: 149-164 (1995).Pulmonary drug delivery is an attractive alternative to oral,transdermal, and parenteral administration because self-administrationis simple, the lungs provide a large mucosal surface for drugabsorption, there is no first-pass liver effect of absorbed drugs, andthere is reduced enzymatic activity and pH mediated drug degradationcompared with the oral route. Relatively high bioavailability of manymolecules, including macromolecules, can be achieved via inhalation.Wall, D. A., Drug Delivery, 2: 1-20 1995); Patton, J. and Platz, R.,Adv. Drug Del. Rev., 8: 179-196 (1992); and Byron, P., Adv. Drug. Del.Rev., 5: 107-132 (1990). As a result, several aerosol formulations oftherapeutic drugs are in use or are being tested for delivery to thelung. Patton, J. S., et al., J. Controlled Release, 28: 79-85 (1994);Damms, B. and Bains, W., Nature Biotechnology (1996); Niven, R. W., etal., Pharm. Res., 12(9): 1343-1349 (1995); and Kobayashi, S., et al.,Pharm. Res., 13(1): 80-83 (1996).

Drugs currently administered by inhalation come primarily as liquidaerosol formulations. However, many drugs and excipients, especiallyproteins, peptides (Liu, R., et al., Biotechnol. Bioeng., 37: 177-184(1991)), and biodegradable carriers such as poly(lactide-co-glycolides)(PLGA), are unstable in aqueous environments for extended periods oftime. This can make storage as a liquid formulation problematic. Inaddition, protein denaturation can occur during aerosolization withliquid formulations. Mumenthaler, M., et al., Pharm. Res., 11: 12-20(1994). Considering these and other limitations, dry powder formulations(DPF's) are gaining increased interest as aerosol formulations forpulmonary delivery. Darnms, B. and W. Bains, Nature Biotechnology(1996); Kobayashi, S., et al, Pharm. Res., 13(1): 80-83 (1996); andTimsina, M., et al., Int. J. Pharm., 101: 1-13 (1994). However, amongthe disadvantages of DPF's is that powders of ultrafine particulatesusually have poor flowability and aerosolization properties, leading torelatively low respirable fractions of aerosol, which are the fractionsof inhaled aerosol that escape deposition in the mouth and throat.Gonda, I., in Topics in Pharmaceutical Sciences 1991, D. Crommelin andK. Midha, Editors, Stuttgart: Medpharm Scientific Publishers, 95-117(1992). A primary concern with many aerosols is particulate aggregationcaused by particle-particle interactions, such as hydrophobic,electrostatic, and capillary interactions.

An effective dry-powder inhalation therapy for both short and long termrelease of therapeutics, either for local or systemic delivery, requiresa powder that displays minimum aggregation, as well as a means ofavoiding or suspending the lung's natural clearance mechanisms untildrugs have been effectively delivered.

One formulation for dry powder pulmonary delivery involves theseparation of active particles from a carrier on actuation of theinhaler. Due to blending requirements, preparing these powders isassociated with an increased number of steps. Furthermore, the method ofdelivery of these powders is associated with several disadvantages. Forexample, there are inefficiencies in the release of active particlesfrom the carrier. Moreover, the carrier takes up significantly morevolume than the active particle, thus high drug doses are difficult toachieve. In addition, the large lactose particles can impact the back ofthe throat, causing coughing.

Therefore, a need exists for dry-powders suitable for inhalation whichminimize or eliminate the above-mentioned problems.

SUMMARY OF THE INVENTION

The invention relates to particles having a tap density of less thanabout 0.4 g/cm³. The particles include an amino acid or a salt thereof.In one embodiment, the particles include a therapeutic, prophylactic ordiagnostic agent or any combination thereof. In another embodiment, theparticles include a phospholipid. In still another embodiment, theparticles have a median geometric diameter of between about 5micrometers and about 30 micrometers. In a further embodiment, theparticles have an aerodynamic diameter of between about 1 and about 5microns.

The invention also relates to a method of producing particles having atap density of less than about 0.4 g/cm³. The method includes forming amixture which includes a therapeutic, prophylactic or diagnostic agent,or any combination thereof, and an amino acid or a salt thereof andspray-drying the mixture to form particles having a tap density of lessthan about 0.4 g/cm³. In one embodiment of the invention, the mixtureincludes a phospholipid. In other embodiments, the mixture includes anorganic solvent or an organic-aqueous co-solvent.

The invention further relates to a method for drug delivery to thepulmonary system. The method includes administering to the respiratorytract of a patient in need of treatment, prophylaxis or diagnosis aneffective amount of particles having a tap density of less than about0.4 g/cm³. The particles include a therapeutic, prophylactic ordiagnostic agent, or any combination thereof, and an amino acid or saltthereof. In one embodiment, the particles include a phosphoglyceride. Inanother embodiment, delivery to the respiratory system includes deliveryto the deep lung. In still another embodiment of the invention, deliveryto the respiratory system includes delivery to the central airways. In afurther embodiment of the invention, delivery to the respiratory systemincludes delivery to the upper airways.

The invention relates also to a composition for drug delivery to thepulmonary system. The composition includes particles which incorporate atherapeutic, prophylactic or diagnostic agent and an amino acid or saltthereof and which have a tap density of less than about 0.4 g/cm³.

Preferred amino acids include hydrophobic amino acids. Examples includebut are not limited to leucine, isoleucine, alanine, valine andphenylalanine. Other amino acids that can be employed are amino acidswhich are insoluble in the solvent system employed to form theparticles.

Preferred phospholipids include but are not limited tophosphatidylcholines, phosphatidylethanolamines, phosphatidylglycerols,phosphatidylserines, phosphatidylinositols and combinations thereof.

The invention has several advantages. For example, the particles of theinvention incorporate amino acids which, in the amounts that areadministered to the respiratory system of a patient, are expected to benon-toxic. Furthermore, amino acids are relatively inexpensive thuslowering overall particle manufacturing costs. Still further, theinvention is capable of conferring extended release properties as wellas improved formulability. In contrast to methods in which activeparticles are released from the carrier on actuation of the inhaler, theentire particles of the invention go to the desired site of thepulmonary system. Drugs can be delivered in higher doses and with higherefficiency. Lodging of particle material in the back of the throat isavoided. The method of forming particles can be carried out usingsimple, inexpensive solvents which do not raise emission and solventrecovery concerns. The method permits the use of Class 3 or bettersolvents. Furthermore, the method requires less process steps thanmethods employed to form powders which release active particles from thecarrier upon actuation of the inhaler.

DETAILED DESCRIPTION OF THE INVENTION

The features and other details of the invention, either as steps of theinvention or as combination of parts of the invention, will now be moreparticularly described and pointed out in the claims. It will beunderstood that the particular embodiments of the invention are shown byway of illustration and not as limitations of the invention. Theprinciple feature of this invention may be employed in variousembodiments without departing from the scope of the invention.

The invention is directed to particles having a tap density of less thanabout 0.4 g/cm³ which include an amino acid or a salt thereof andmethods of producing such particles. The invention is also directed tomethods of delivering the particles to the pulmonary system of apatient.

In a preferred embodiment the amino acid is hydrophobic. Suitablehydrophobic amino acids include naturally occurring and non-naturallyoccurring hydrophobic amino acids. Non-naturally occuring amino acidsinclude, for example, beta-amino acids, Both D, L and racemicconfigurations of hydrophobic amino acids can be employed. Suitablehydrophobic amino acids can also include amino acid analogs. As usedherein, an amino acid analog includes the D or L configuration of anamino acid having the following formula: —NH—CHR—CO—, wherein R is analiphatic group, a substituted aliphatic group, a benzyl group, asubstituted benzyl group, an aromatic group or a substituted aromaticgroup and wherein R does not correspond to the side chain of anaturally-occurring amino acid. As used herein, aliphatic groups includestraight chained, branched or cyclic C1-C8 hydrocarbons which arecompletely saturated, which contain one or two heteroatoms such asnitrogen, oxygen or sulfur and/or which contain one or more units ofunsaturation. Aromatic groups include carbocyclic aromatic groups suchas phenyl and naphthyl and heterocyclic aromatic groups such asimidazolyl, indolyl, thienyl, furanyl, pyridyl, pyranyl, pyranyl,oxazolyl, benzothienyl, benzofuranyl, quinolinyl, isoquinolinyl andacridintyl.

Suitable substituents on an aliphatic, aromatic or benzyl group include—OH, halogen (—Br, —Cl, —I and —F) —O(aliphatic, substituted aliphatic,benzyl, substituted benzyl, aryl or substituted aryl group), —CN, —NO₂,—COOH, —NH₂, —NH(aliphatic group, substituted aliphatic, benzyl,substituted benzyl, aryl or substituted aryl group), —N(aliphatic group,substituted aliphatic, benzyl, substituted benzyl, aryl or substitutedaryl group)₂, —COO(aliphatic group, substituted aliphatic, benzyl,substituted benzyl, aryl or substituted aryl group), —CONH₂,—CONH(aliphatic, substituted aliphatic group, benzyl, substitutedbenzyl, aryl or substituted aryl group)), —SH, —S(aliphatic, substitutedaliphatic, benzyl, substituted benzyl, aromatic or substituted aromaticgroup) and —NH—C(═NH)—NH₂. A substituted benzylic or aromatic group canalso have an aliphatic or substituted aliphatic group as a substituent.A substituted aliphatic group can also have a benzyl, substitutedbenzyl, aryl or substituted aryl group as a substituent. A substitutedaliphatic, substituted aromatic or substituted benzyl group can have oneor more substituents. Modifying an amino acid substituent can increase,for example, the lypophilicity or hydrophobicity of natural amino acidswhich are hydrophillic.

A number of the suitable amino acids, amino acids analogs and saltsthereof can be obtained commercially. Others can be synthesized bymethods known in the art. Synthetic techniques are described, forexample, in Green and Wuts, “Protecting Groups in Organic Synthesis”,John Wiley and Sons, Chapters 5 and 7, 1991.

Hydrophobicity is generally defined with respect to the partition of anamino acid between a nonpolar solvent and water. Hydrophobic amino acidsare those acids which show a preference for the nonpolar solvent.Relative hydrophobicity of amino acids can be expressed on ahydrophobicity scale on which glycine has the value 0.5. On such ascale, amino acids which have a preference for water have values below0.5 and those that have a preference for nonpolar solvents have a valueabove 0.5. As used herein, the term hydrophobic amino acid refers to anamino acid that, on the hydrophobicity scale has a value greater orequal to 0.5, in other words, has a tendency to partition in thenonpolar acid which is at least equal to that of glycine.

Examples of amino acids which can be employed include, but are notlimited to: glycine, proline, alanine, cysteine, methionine, valine,leucine, tyrosine, isoleucine, phenylalanine, tryptophan. Preferredhydrophobic amino acids include leucine, isoleucine, alanine, valine,phenylalanine and glycine. Combinations of hydrophobic amino acids canalso be employed. Furthermore, combinations of hydrophobic andhydrophilic (preferentially partitioning in water) amino acids, wherethe overall combination is hydrophobic, can also be employed.

In a preferred embodiment of the invention, the amino acid is insolublein the solvent system employed, such as, for example, in a 70:30(vol/vol) ethanol:water co-solvent.

The amino acid can be present in the particles of the invention in anamount of at least 10 weight %. Preferably, the amino acid can bepresent in the particles in an amount ranging from about 20 to about 80weight %. The salt of a hydrophobic amino acid can be present in theparticles of the invention in an amount of at least 10% weight.Preferably, the amino acid salt is present in the particles in an amountranging from about 20 to about 80 weight %.

Examples of therapeutic, prophylactic or diagnostic agents includesynthetic inorganic and organic compounds, proteins, peptides,polypeptides, polysaccharides and other sugars, lipids, and DNA and RNAnucleic acid sequences having therapeutic, prophylactic or diagnosticactivities. Nucleic acid sequences include genes, antisense moleculeswhich bind to complementary DNA or RNA and inhibit transcription, andribozymes. The agents to be incorporated can have a variety ofbiological activities, such as vasoactive agents, neuroactive agents,hormones, anticoagulants, immunomodulating agents, cytotoxic agents,prophylactic agents, antibiotics, antivirals, antisense, antigens, andantibodies. In some instances, the proteins may be antibodies orantigens which otherwise would have to be administered by injection toelicit an appropriate response. Compounds with a wide range of molecularweight can be encapsulated, for example, between 100 and 500,000 gramsor more per mole.

The particles can include a therapeutic agent for local delivery withinthe lung, such as agents for the treatment of asthma, emphysema, orcystic fibrosis, or for systemic treatment. For example, genes for thetreatment of diseases such as cystic fibrosis can be administered, ascan beta agonists for asthma. Other specific therapeutic agents include,but are not limited to, human growth hormone, insulin, calcitonin,leuprolide (or gonadotropin-releasing hormone (“LHRH”)), granulocytecolony-stimulating factor (“G-CSF”), parathyroid hormone-relatedpeptide, somatostatin, testosterone, progesterone, estradiol, nicotine,fentanyl, norethisterone, clonidine, scopolamine, salicylate, cromolynsodium, salmeterol, formeterol, albuterol, and Valium.

Any of a variety of diagnostic agents can be incorporated within theparticles, which can locally or systemically deliver the incorporatedagents following administration to a patient. Biocompatible orpharmacologically acceptable gases can be incorporated into theparticles or trapped in the pores of the particles using technologyknown to those skilled in the art. The term gas refers to any compoundwhich is a gas or capable of forming a gas at the temperature at whichimaging is being performed. In one embodiment, retention of gas in theparticles is improved by forming a gas-impermeable barrier around theparticles. Such barriers are well known to those of skill in the art.

Diagnostic agents also include but are not limited to imaging agentswhich include commercially available agents used in positron emissiontomography (PET), computer assisted tomography (CAT), single photonemission computerized tomography, x-ray, fluoroscopy, and magneticresonance imaging (MRI).

Examples of suitable materials for use as contrast agents in MRI includebut are not limited to the gadolinium chelates currently available, suchas diethylene triamine pentacetic acid (DTPA) and gadopentotatedimeglumine, as well as iron, magnesium, manganese, copper and chromium.

Examples of materials useful for CAT and x-rays include iodine basedmaterials for intravenous administration, such as ionic monomerstypified by diatrizoate and iothalamate, non-ionic monomers such asiopamidol, isohexol, and ioversol, non-ionic dimers, such as iotrol andiodixanol, and ionic dimers, for example, ioxagalte.

The particles of the invention can also be precursors to tabletformulations.

Preferably, a therapeutic, prophylactic, diagnostic agent or acombination thereof can be present in the spray-dried particles in anamount ranging from less than about 1 weight % to about 90 weight %.

In another embodiment of the invention, the particles include aphospholipid, also referred to herein as phosphoglyceride. In apreferred embodiment, the phospholipid, is endogenous to the lung. Inanother preferred embodiment the phospholipid includes, among others,phosphatidylcholines, phosphatidylethanolamines, phosphatidylglycerols,phosphatidylserines, phosphatidylinositols and combinations thereof.Specific examples of phospholipids include but are not limited tophosphatidylcholines dipalmitoyl phosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), distearoyl phosphatidylcholine (DSPC),dipalmitoyl phosphatidyl glycerol (DPPG) or any combination thereof.

The phospholipid, can be present in the particles in an amount rangingfrom about 0 to about 90 weight %. Preferably, it can be present in theparticles in an amount ranging from about 10 to about 60 weight %.

In still another embodiment of the invention the particles include asurfactant such as, but not limited to the phospholipids describedabove. Other surfactants, such as, for example, hexadecanol; fattyalcohols such as polyethylene glycol (PEG); polyoxyethylene-9-laurylether; a surface active fatty acid, such as palmitic acid or oleic acid;glycocholate; surfactin; a poloxomer; a sorbitan fatty acid ester suchas sorbitan trioleate (Span 85); tyloxapol can also be employed.

As used herein, the term “surfactant” refers to any agent whichpreferentially absorbs to an interface between two immiscible phases,such as the interface between water and an organic polymer solution, awater/air interface or organic solvent/air interface. Surfactantsgenerally possess a hydrophilic moiety and a lipophilic moiety, suchthat, upon absorbing to microparticles, they tend to present moieties tothe external environment that do not attract similarly-coated particles,thus reducing particle agglomeration. Surfactants may also promoteabsorption of a therapeutic or diagnostic agent and increasebioavailability of the agent.

The surfactant can be present in the particles in an amount ranging fromabout 0 to about 90 weight %. Preferably, it can be present in theparticles in an amount ranging from about 10 to about 60 weight %.

The a preferred embodiment of the invention, the particles include atherapeutic, prophylactic or diagnostic agent, or combinations thereof,a hydrophobic amino acid or a salt thereof, and a phospholipid.

In one embodiment of the invention, the phospholipid or combination orphospholipids present in the particles can have a therapeutic,prophylactic or diagnostic role. For example, the particles of theinvention can be used to deliver surfactants to the lung of a patient.This is particularly useful in medical indications which requiresupplementing or replacing endogenous lung surfactants, for example inthe case of infant respiratory distress syndrome.

The particles of the invention can also include one or more compoundsemployed in controlled or sustained release formulations. For example,the spray-dried particles can include a biocompatible, and preferablybiodegradable polymer, copolymer, or blend. Preferred polymers are thosewhich are capable of forming aerodynamically light particles having atap density less than about 0.4 g/cm³, a mean diameter between about 5μm and about 30 μm and an aerodynamic diameter between approximately oneand five microns, preferably between about one and about three microns.The polymers can be tailored to optimize different characteristics ofthe particle including: i) interactions between the agent to bedelivered and the polymer to provide stabilization of the agent andretention of activity upon delivery; ii) rate of polymer degradationand, thereby, rate of drug release profiles; iii) surfacecharacteristics and targeting capabilities via chemical modification;and iv) particle porosity.

Surface eroding polymers such as polyanhydrides can be used to form theparticles. For example, polyanhydrides such aspoly[(p-carboxyphenoxy)-hexane anhydride] (PCPH) may be used. Suitablebiodegradable polyanhydrides are described in U.S. Pat. No. 4,857,311.

In another embodiment, bulk eroding polymers such as those based onpolyesters including poly(hydroxy acids) can be used. For example,polyglycolic acid (PGA), polylactic acid (PLA), or copolymers thereofmay be used to form the particles. The polyester may also have a chargedor functionalizable group, such as an amino acid. In a preferredembodiment, particles with controlled release properties can be formedof poly(D,L-lactic acid) and/or poly(D,L-lactic-co-glycolic acid)(“PLGA”) which incorporate a phospholipid such as DPPC.

Still other polymers include but are not limited to polyamides,polycarbonates, polyalkylenes such as polyethylene, polypropylene,poly(ethylene glycol), poly(ethylene oxide), poly(ethyleneterephthalate), poly vinyl compounds such as polyvinyl alcohols,polyvinyl ethers, and polyvinyl esters, polymers of acrylic andmethacrylic acids, celluloses and other polysaccharides, and peptides orproteins, or copolymers or blends thereof. Polymers may be selected withor modified to have the appropriate stability and degradation rates invivo for different controlled drug delivery applications.

In one embodiment, the particles include functionalized polyester graftcopolymers, as described in Hrkach et al., Macromolecules, 28: 4736-4739(1995); and Hrkach et al., “Poly(L-Lactic acid-co-amino acid) GraftCopolymers: A Class of Functional Biodegradable Biomaterials” inHydrogels and Biodegradable Polymers for Bioapplications, ACS SymposiumSeries No. 627, Raphael M. Ottenbrite et al., Eds., American ChemicalSociety, Chapter 8, pp. 93-101, 1996.

Materials other than biodegradable polymers can be included in thespray-dried particles of the invention. Suitable materials includevarious non-biodegradable polymers and various excipients. Examples ofexcipients include, but are not limited to: a sugar, such as lactose,polysaccharides, cyclodextrins and/or a surfactant.

The particles of the invention can be employed in compositions suitablefor drug delivery to the pulmonary system. For example, suchcompositions can include the particles and a pharmaceutically acceptablecarrier for administration to a patient, preferably for administrationvia inhalation. The particles can be co-delivered, for example, withlarger carrier particles, not carrying a therapeutic agent, having, forexample, a mean diameter ranging between about 50 μm and about 100 μm.

The particles of the invention have a tap density less than about 0.4g/cm³. As used herein, the phrase “aerodynamically light particles”refers to particles having a tap density less than about 0.4 g/cm³. Thetap density of particles of a dry powder can be obtained using a GeoPyc™instrument (Micrometrics Instrument Corp., Norcross, Ga. 30093). A DualPlatform Microprocessor Controlled Tap Density Tester (Vankel, N.C.) canalso be used. Tap density is a standard measure of the envelope massdensity. The envelope mass density of an isotropic particle is definedas the mass of the particle divided by the minimum sphere envelopevolume within which it can be enclosed. Features which can contribute tolow tap density include irregular surface texture and porous structure.

The preferred median diameter for aerodynamically light particles forinhalation therapy is at least about 5 microns (μm), for example betweenabout 5 and about 30 μm. Terms such as median diameter, mass mediandiameter (MMD), mass median geometric diameter (MMGD) and mass medianenvelope diameter (MMED) are herein used interchangeably. The termdiameter, in contrast with the term “aerodynamic diameter”, refersherein to mass or geometric diameter. The terms “aerodynamic diameter”and “mass median aerodynamic diameter” (MMAD) are used hereininterchangeably. In one embodiment of the invention, the mass medianaerodynamic diameter is between about 1 μm and about 5 μm. In anotherembodiment of the invention, the mass median aerodynamic diameter isbetween about 1 μm and about 3 μm. In a further embodiment, the massmedian aerodynamic diameter is between about 3 μm and about 5 μm.

The mass median diameter of the spray-dried particles can be measuredusing an electrical zone sensing instrument such as a Multisizer IIe,(Coulter Corp., Miami, Fla.), or a laser diffraction instrument (forexample Helos, manufactured by Sympatec, Princeton, N.J.). The diameterof particles in a sample will range depending upon factors such asparticle composition and methods of synthesis. The distribution of sizeof particles in a sample can be selected to permit optimal depositionwithin targeted sites within the respiratory tract.

Process conditions as well as efficiency of inhaler, in particular withrespect to dispersibility, can contribute to the size of particles thatcan be delivered to the pulmonary system.

Aerodynamically light particles may be fabricated or separated, forexample by filtration or centrifugation, to provide a particle samplewith a preselected size distribution. For example, greater than about30%, 50%, 70%, or 80% of the particles in a sample can have a diameterwithin a selected range of at least about 5 μm. The selected rangewithin which a certain percentage of the particles must fall may be forexample, between about 5 and about 30 μm, or optimally between about 5and about 15 μm. In one preferred embodiment, at least a portion of theparticles have a diameter between about 9 and about 11 μm. Optionally,the particle sample also can be fabricated wherein at least about 90%,or optionally about 95% or about 99%, have a diameter within theselected range. The presence of the higher proportion of theaerodynamically light, larger diameter particles in the particle sampleenhances the delivery of therapeutic or diagnostic agents incorporatedtherein to the deep lung. Large diameter particles generally meanparticles having a median geometric diameter of at least about 5 μm.

Aerodynamically light particles with a tap density less than about 0.4g/cm³, median diameters of at least about 5 μm, and an aerodynamicdiameter of between about 1 and about 5 μm, preferably between about 1and about 3 μm, are more capable of escaping inertial and gravitationaldeposition in the oropharyngeal region, and are targeted to the airwaysor the deep lung. The use of larger, more porous particles isadvantageous since they are able to aerosolize more efficiently thansmaller, denser aerosol particles such as those currently used forinhalation therapies.

In comparison to smaller, relatively denser particles the largeraerodynamically light particles, preferably having a median diameter ofat least about 5 μm, also can potentially more successfully avoidphagocytic engulfment by alveolar macrophages and clearance from thelungs, due to size exclusion of the particles from the phagocytes'cytosolic space. Phagocytosis of particles by alveolar macrophagesdiminishes precipitously as particle diameter increases beyond about 3μm. Kawaguchi, H., et al., Biomaterials 7: 61-66 (1986); Krenis, L. J.and Strauss, B., Proc. Soc. Exp. Med., 107: 748-750 (1961); and Rudt, S.and Muller, R. H., J. Contr. Rel., 22: 263-272 (1992). For particles ofstatistically isotropic shape, such as spheres with rough surfaces, theparticle envelope volume is approximately equivalent to the volume ofcytosolic space required within a macrophage for complete particlephagocytosis.

Aerodynamically light particles thus are capable of a longer termrelease of an encapsulated agent in the lungs. Following inhalation,aerodynamically light biodegradable particles can deposit in the lungs,and subsequently undergo slow degradation and drug release, without themajority of the particles being phagocytosed by alveolar macrophages.The drug can be delivered relatively slowly into the alveolar fluid, andat a controlled rate into the blood stream, minimizing possible toxicresponses of exposed cells to an excessively high concentration of thedrug. The aerodynamically light particles thus are highly suitable forinhalation therapies, particularly in controlled release applications.

The particles may be fabricated with the appropriate material, surfaceroughness, diameter and tap density for localized delivery to selectedregions of the respiratory tract such as the deep lung or upper orcentral airways. For example, higher density or larger particles may beused for upper airway delivery, or a mixture of varying sized particlesin a sample, provided with the same or different therapeutic agent maybe administered to target different regions of the lung in oneadministration. Particles having an aerodynamic diameter ranging fromabout 3 to about 5 μm are preferred for delivery to the central andupper airways. Particles having and aerodynamic diameter ranging fromabout 1 to about 3 μm are preferred for delivery to the deep lung.

Inertial impaction and gravitational settling of aerosols arepredominant deposition mechanisms in the airways and acini of the lungsduring normal breathing conditions. Edwards, D. A., J. Aerosol Sci., 26:293-317 (1995). The importance of both deposition mechanisms increasesin proportion to the mass of aerosols and not to particle (or envelope)volume. Since the site of aerosol deposition in the lungs is determinedby the mass of the aerosol (at least for particles of mean aerodynamicdiameter greater than approximately 1 μm), diminishing the tap densityby increasing particle surface irregularities and particle porositypermits the delivery of larger particle envelope volumes into the lungs,all other physical parameters being equal.

The low tap density particles have a small aerodynamic diameter incomparison to the actual envelope sphere diameter. The aerodynamicdiameter, d_(aer), is related to the envelope sphere diameter, d (Gonda,I., “Physico-chemical principles in aerosol delivery,” in Topics inPharmaceutical Sciences 1991 (eds. D. J. A. Crommelin and K. K. Midha),pp. 95-117, Stuttgart: Medpharm Scientific Publishers, 1992)), by theformula:

d _(aer) =dρ

where the envelope mass ρ is in units of g/cm³. Maximal deposition ofmonodispersed aerosol particles in the alveolar region of the human lung(˜60%) occurs for an aerodynamic diameter of approximately d_(aer)=3 μm.Heyder, J. et al., J. Aerosol Sci., 17: 811-825 (1986). Due to theirsmall envelope mass density, the actual diameter d of aerodynamicallylight particles comprising a monodisperse inhaled powder that willexhibit maximum deep-lung deposition is:

d=3/ρ μm (where ρ<1 g/cm³);

where d is always greater than 3 μm. For example, aerodynamically lightparticles that display an envelope mass density, ρ=0.1 g/cm³, willexhibit a maximum deposition for particles having envelope diameters aslarge as 9.5 μm. The increased particle size diminishes interparticleadhesion forces. Visser, J., Powder Technology, 58: 1-10. Thus, largeparticle size increases efficiency of aerosolization to the deep lungfor particles of low envelope mass density, in addition to contributingto lower phagocytic losses.

In one embodiment of the invention, the spray-dried particles have a tapdensity less than about 0.4 g/cm³ and a median diameter between about 5μm and about 30 μm, which in combination yield an aerodynamic diameterof between about 1 and about 5 μm, and for delivery to the deep lung,preferably between about 1 and about 3 μm. The aerodyanamic diameter iscalculated to provide for maximum deposition within the lungs,previously achieved by the use of very small particles of less thanabout five microns in diameter, preferably between about one and aboutthree microns, which are then subject to phagocytosis. Selection ofparticles which have a larger diameter, but which are sufficiently light(hence the characterization “aerodynamically light”), results in anequivalent delivery to the lungs, but the larger size particles are notphagocytosed. Improved delivery can be obtained by using particles witha rough or uneven surface relative to those with a smooth surface.

In another embodiment of the invention, the particles have a massdensity of less than about 0.4 g/cm³ and a mean diameter of betweenabout 5 μm and about 30 μm. Mass density and the relationship betweenmass density, mean diameter and aerodynamic diameter are discussed inU.S. application Ser. No. 08/655,570, filed on May 24, 1996, which isincorporated herein by reference in its entirety. In a preferredembodiment, the aerodynamic diameter of particles having a mass densityless than about 0.4 g/cm³ and a mean diameter of between about 5 μm andabout 30 μm is between about 1 μm and about 5 μm.

The invention also relates to methods of preparing particles having atap density less than about 0.4 g/cm³. In one embodiment, the methodincludes forming a mixture including a therapeutic, prophylactic ordiagnostic agent, or a combination thereof, and an amino acid or a saltthereof. The therapeutic, prophylactic or diagnostic agents which can beemployed include but are not limited to those described above. The aminoacids or salts thereof, include but are not limited to those describedbefore.

In a preferred embodiment, the mixture includes a surfactant, such as,for example, the surfactants described above. In another preferredembodiment, the mixture includes a phospholipid, such as, for examplethe phospholipids described above. An organic solvent or anaqueous-organic solvent can be employed to form the mixture.

Suitable organic solvents that can be employed include but are notlimited to alcohols such as, for example, ethanol, methanol, propanol,isopropanol, butanols, and others. Other organic solvents include butare not limited to perfluorocarbons, dichloromethane, chloroform, ether,ethyl acetate, methyl tert-butyl ether and others.

Co-solvents that can be employed include an aqueous solvent and anorganic solvent, such as, but not limited to, the organic solvents asdescribed above. Aqueous solvents include water and buffered solutions.In one embodiment, an ethanol water solvent is preferred with theethanol:water ratio ranging from about 50:50 to about 90:10ethanol:water.

The mixture can have a neutral, acidic or alkaline pH. Optionally, a pHbuffer can be added to the solvent or co-solvent or to the formedmixture. Preferably, the pH can range from about 3 to about 10.

The mixture is spray-dried. Suitable spray-drying techniques aredescribed, for example, by K. Masters in “Spray Drying Handbook”, JohnWiley & Sons, New York, 1984. Generally, during spray-drying, heat froma hot gas such as heated air or nitrogen is used to evaporate thesolvent from droplets formed by atomizing a continuous liquid feed.

In a preferred embodiment, a rotary atomizer is employed. An examples ofsuitable spray driers using rotary atomization includes the Mobile Minorspray drier, manufactured by Niro, Denmark. The hot gas can be, forexample, air, nitrogen or argon.

Without being held to any particular theory, it is believed that due totheir hydrophobicity and low water solubility, hydrophobic amino acidsfacilitate the formation of a shell during the drying process when anethanol:water co-solvent is employed. It is also believed that the aminoacids may alter the phase behavior of the phospholipids in such a way asto facilitate the formation of a shell during the drying process.

The particles of the invention can be used for delivery to the pulmonarysystem. They can be used to provide controlled systemic or localdelivery of therapeutic or diagnostic agents to the respiratory tractvia aerosolization. Administration of the particles to the lung byaerosolization permits deep lung delivery of relatively large diametertherapeutic aerosols, for example, greater than about 5 μm in mediandiameter. The particles can be fabricated with a rough surface textureto reduce particle agglomeration and improve flowability of the powder.The spray-dried particles have improved aerosolization properties. Thespray-dried particle can be fabricated with features which enhanceaerosolization via dry powder inhaler devices, and lead to lowerdeposition in the mouth, throat and inhaler device.

The particles may be administered alone or in any appropriatepharmaceutically acceptable carrier, such as a liquid, for examplesaline, or a powder, for administration to the respiratory system. Theycan be co-delivered with larger carrier particles, not including atherapeutic agent, the latter possessing mass median diameters forexample in the range between about 50 μm and about 100 μm.

Aerosol dosage, formulations and delivery systems may be selected for aparticular therapeutic application, as described, for example, in Gonda,I. “Aerosols for delivery of therapeutic and diagnostic agents to therespiratory tract,” in Critical Reviews in Therapeutic Drug CarrierSystems, 6: 273-313, 1990; and in Moren, “Aerosol dosage forms andformulations,” in: Aerosols in Medicine. Principles. Diagnosis andTherapy, Moren, et al., Eds, Esevier, Amsterdam, 1985.

The use of biodegradable polymers permits controlled release in thelungs and long-time local action or systemic bioavailability.Denaturation of macromolecular drugs can be minimized duringaerosolization since macromolecules can be contained and protectedwithin a polymeric shell. Coencapsulation of peptides withpeptidase-inhibitors can minimize peptide enzymatic degradation.Pulmonary delivery advantageously can reduce or eliminate the need forinjection. For example, the requirement for daily insulin injections canbe avoided.

The invention is also related to a method for drug delivery to thepulmonary system. The method comprises administering to the respiratorytract of a patient in need of treatment, prophylaxis or diagnosis aneffective amount of particles comprising a therapeutic, prophylactic ordiagnostic agent and a hydrophobic amino acid. In a preferredembodiment, the particles include a phospholipid. As used herein, theterm “effective amount” means the amount needed to achieve the desiredeffect or efficacy.

Porous or aerodynamically light particles, having a geometric size (ormean diameter) in the range of about 5 to about 30 μm, and tap densityless than about 0.4 g/cm³, such that they possess an aerodynamicdiameter of about 1 and about 3 μm, have been shown to display idealproperties for delivery to the deep lung. Larger aerodynamic diameters,ranging, for example, from about 3 to about 5 μm are preferred, however,for delivery to the central and upper airways. According to oneembodiment of the invention the particles have a tap density of lessthan about 0.4 g/cm³ and a mean diameter of between about 5 μm and about30 μm. According to another embodiment of the invention, the particleshave a mass density of less than about 0.4 g/cm³ and a mean diameter ofbetween about 5 μm and about 30 μm. In one embodiment of the invention,the particles have an aerodynamic diameter between about 1 μm and about5 μm. In another embodiment of the invention, the particles have anaerodynamic diameter between about 1 μm and about 3 μm microns. In stillanother embodiment of the invention, the particles have an aerodynamicdiameter between about 3 μm and about 5 μm.

For therapeutic, diagnosis or prophylactic use, particles can bedelivered from an inhaler device, such as but not limited to ametered-dose-inhaler (MDI), dry-powder inhaler (DPI), nebulizer or byinstillation. Such devices are known in the art. For example, a DPI isdescribed in U.S. Pat. No. 4,069,819 issued to Valentini, et al. on Aug.5, 1976.

The present invention will be further understood by reference to thefollowing non-limiting examples.

EXEMPLIFICATIONS

Some of the methods and materials employed in the following examples aredescribed in U.S. application Ser. No. 09/211,940, filed Dec. 15, 1998,in U.S. application Ser. No. 08/739,308, filed Oct. 29, 1996, now U.S.Pat. No. 5,874,064, in U.S. application Ser. No. 08/655,570, filed May24, 1996, in U.S. application Ser. No. 09/194,068, filed May 23, 1997,in PCT/US97/08895 application filed May 23, 1997, in U.S. applicationSer. 08/971,791, filed Nov. 17, 1997, in U.S. application Ser. No.08/784,421, filed Jan. 16, 1997, now U.S. Pat. No. 5,855,913 and in U.S.application Ser. No. 09/337,245, filed on Jun. 22, 1999, all of whichare incorporated herein by reference in their entirety.

Materials

Leucine was obtained from Spectrum Chemical Company. DPPC was obtainedfrom Avanti Polar Lipids (Alabaster, Ala.).

Spray Drying

A Mobile Minor spray-drier from Niro was used. The gas employed wasdehumidified air. The gas temperature ranged from about 80 to about 150°C. The atomizer speed ranged from about 15,000 to about 50,000 RPM. Thegas rate was 70 to 92 kg/hour and the liquid feed rate ranged from about50 to about 100 ml/minute.

Geometric Size Distribution Analysis

Size distributions were determined using a Coulter Multisizer II.Approximately 5-10 mg of powder was added to 50 mL isoton II solutionuntil the coincidence of particles was between 5 and 8%. Greater than500,000 particles were counted for each batch of spheres.

Aerodynamic Size Distribution Analysis

Aerodynamic size distribution was determined using anAerosizer/Aerodispenser (Amherst Process Instruments, Amherst, Mass.).Approximately 2 mg powder was introduced into the Aerodisperser and theAerodynamic size was determined by time of flight measurements.

EXAMPLE 1

A mixture including 40 weight % of an amino acid and 60 weight % DPPCwas formed in a 70/30 vol/vol ethanol-water co-solvent and spray-dried.The results are shown in Table 1.

Table 1 shows median geometric and aerodynamic diameters for particlesincluding several amino acids, their hydrophobicity and estimated tapdensity. Tap density was estimated using the equation discussed above.

TABLE 1 Amino acid hydrophobicity MMGD MMAD Est. tap density Leucine0.943 7.9 3.0 0.11 Isleucine 0.943 8.1 2.7 0.14 Phenylalanine 0.501 7.93.8 0.23 Glutamine 0.251 6.5 4.4 0.45 Glutamate 0.043 5.1 4.1 0.64

EXAMPLE 2

Particles containing albuterol sulfate were prepared in the followingmanner. A mixture including 76% DSPC, 20% leucine and 4% albuterolsulfate was formed in a 70/30 (v/v) ethanol/water co-solvent and spraydried. The mass median geometric diameter of the resulting particles was8.2 μm and the mass median aerodynamic diameter was 2.8 μm.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method for drug delivery to the respiratorysystem comprising: administering to the respiratory tract of a patientin need of treatment, prophylaxis or diagnosis an effective amount ofspray dried particles wherein said particles consist of a therapeutic,prophylactic or diagnostic agent, or any combination thereof, an aminoacid or salt thereof, and a phospholipid or combination of phospholipidsand wherein the particles have a tap density less than about 0.4 g/cm³.2. The method of claim 1 wherein the particles have a median geometricdiameter of between about 5 microns and about 30 microns.
 3. The methodof claim 1 wherein the particles have an aerodynamic diameter of betweenabout 1 and about 5 microns.
 4. The method of claim 1 wherein theparticles have an aerodynamic diameter of between about 1 and about 3microns.
 5. The method of claim 1 wherein the particles have anaerodynamic diameter of between about 3 and about 5 microns.
 6. Themethod of claim 1 wherein delivery to the pulmonary system includesdelivery to the deep lung.
 7. The method of claim 1 wherein delivery tothe pulmonary system includes delivery to the central airways.
 8. Themethod of claim 1 wherein delivery to the pulmonary system includesdelivery to the upper airways.
 9. The method of claim 1 wherein theamino acid is hydrophobic.
 10. The method of claim 1 wherein the aminoacid is selected from the group consisting of leucine, isoleucine,alanine, valine and phenylalanine.
 11. The method of claim 10 whereinthe amino acid is leucine.
 12. The method of claim 1 wherein the aminoacid or salt thereof is present in the particles in an amount of atleast 10% by weight.
 13. The method of claim 1 wherein the therapeutic,prophylactic or diagnostic agent is present in the particles in anamount ranging from about 1% to about 90% by weight.
 14. The method ofclaim 1 wherein the phospholipid is endogenous to the lung.
 15. Themethod of claim 1 wherein the phospholipid is selected from the groupconsisting of phosphatidylcholines, phosphatidylethanolamines,phosphatidylglycerols, phosphatidylserines, phosphatidylinositols andcombinations thereof.
 16. The method of claim 1 wherein the therapeutic,prophylactic or diagnostic agent is selected from the group consistingof salmeterol, formoterol and albuterol.
 17. The method of claim 16wherein the therapeutic agent is albuterol.
 18. Spray dried particlesconsisting of a therapeutic, prophylactic or diagnostic agent, or anycombination thereof, an amino acid or salt thereof, and a phospholipidor combination of phospholipids; wherein the particles have a tapdensity less than about 0.4 g/cm³.
 19. The particles of claim 18 whereinthe particles have a median geometric diameter of between about 5microns and about 30 microns.
 20. The particles of claim 18 wherein theparticles have an aerodynamic diameter of between about 1 and about 5microns.
 21. The particles of claim 18 wherein the particles have anaerodynamic diameter of between about 1 and about 3 microns.
 22. Theparticles of claim 18 wherein the particles have an aerodynamic diameterof between about 3 and about 5 microns.
 23. The particles of claim 18wherein the amino acid is hydrophobic.
 24. The particles of claim 18wherein the amino acid is selected from a group consisting of leucine,isoleucine, alanine, valine, phenylalanine and combinations thereof. 25.The particles of claim 24 wherein the amino acid is leucine.
 26. Theparticles of claim 18 wherein the amino acid or salt thereof is presentin the particles in an amount of at least 10% by weight.
 27. Theparticles of claim 18 wherein the therapeutic, prophylactic ordiagnostic agent is present in the particles in an amount ranging fromabout 1% to about 90% by weight.
 28. The particles of claim 18 whereinthe phospholipid is endogenous to the lung.
 29. The particles of claim18 wherein the phospholipid is selected from the group consisting ofphosphatidylcholines, phosphatidylethanolamines, phosphatidylglycerols,phosphatidylserines, phosphatidylinositols and combinations thereof. 30.The particles of claim 18 wherein the therapeutic, prophylactic ordiagnostic agent is selected from the group consisting of salmeterol,formoterol and albuterol.
 31. The particles of claim 30 wherein thetherapeutic agent is albuterol.